HDR.fas

BackgroundIsoprenoids are the most ancient and essential class of metabolites produced in all organisms, either via mevalonate (MVA)-and/or methylerythritol phosphate (MEP)-pathways. The MEP-pathway is present in all plastid-bearing organisms and most eubacteria. However, no comprehensive study reveals the origination and evolutionary characteristics of MEP-pathway genes in eukaryotes.ResultsHere, detailed bioinformatics analyses of the MEP-pathway provide an in-depth understanding the evolutionary history of this indispensable biochemical route, and offer a basis for the co-existence of the cytosolic MVA- and plastidial MEP-pathway in plants given the established exchange of the end products between the two isoprenoid-biosynthesis pathways. Here, phylogenetic analyses establish the contributions of both cyanobacteria and Chlamydiae sequences to the plant’s MEP-pathway genes. Moreover, Phylogenetic and inter-species syntenic block analyses demonstrate that six of the seven MEP-pathway genes have predominantly remained as single-copy in land plants in spite of multiple whole-genome duplication events (WGDs). Substitution rate and domain studies display the evolutionary conservation of these genes, reinforced by their high expression levels. Distinct phenotypic variation among plants with reduced expression levels of individual MEP-pathway genes confirm the indispensable function of each nuclear-encoded plastid-targeted MEP-pathway enzyme in plant growth and development.ConclusionCollectively, these findings reveal the polyphyletic origin and restrict conservation of MEP-pathway genes, and reinforce the potential function of the individual enzymes beyond production of the isoprenoids intermediates.

背景异戊二烯类物质是所有生物体中最为古老且至关重要的代谢物类别，其生成途径包括通过异戊二烯酸（MVA）途径及/或甲基赤藓糖-4-磷酸（MEP）途径。MEP途径存在于所有含质体的生物体以及大多数真细菌中。然而，迄今为止，尚无全面的研究揭示真核生物中MEP途径基因的起源和进化特征。结果在此，我们对MEP途径进行了深入的生物信息学分析，揭示了这一不可或缺的生物化学途径的进化历史，并为植物中胞质MVA途径与质体MEP途径共存提供了理论依据，鉴于两种异戊二烯生物合成途径之间已确立的终产物交换。在此，系统发育分析确立了蓝细菌和支原体序列对植物MEP途径基因的贡献。此外，系统发育和种间同源连锁块分析表明，尽管经历了多次全基因组复制事件（WGDs），七个MEP途径基因中的六个在陆生植物中仍以单拷贝为主。替代速率和结构域研究显示出这些基因的进化保守性，其高表达水平进一步强化了这一观点。具有单个MEP途径基因表达水平降低的植物在表型上的差异，证实了每个核编码的质体靶向MEP途径酶在植物生长和发育中的不可或缺功能。结论综合来看，这些发现揭示了MEP途径基因的多系起源和限制性保守性，并强化了这些酶在异戊二烯中间体生产之外的潜在功能。（MEP-pathway, MVA, MEP, eubacteria, phylogenetic, WGDs, substitution rate, domain, plastid-targeted, phenotypic variation）